Thin films transparent for a light in the visible light region and having electric conductivity are generally used in display systems, e.g., a liquid crystal display and an electroluminescence display, transparent electrodes, e.g., a touch panel, and for the static prevention and cutoff of electromagnetic waves of transparent articles. As such a transparent conductive thin film, so-called conductive glass comprising a glass plate having formed thereon an indium oxide thin film is conventionally used. However, since glass is used as a base, the conductive glass is inferior in flexibility and processability and cannot be used in some cases according to uses.
Therefore, in recent years, conductive thin films using various kinds of plastic films including polyethylene terephthalate as the base are used for various advantages, e.g., flexibility, processability, impact resistance and light weight (refer to reference 1 and 2).
However, these kinds of conductive thin films are great in the reflectance of light of the thin film surface, so that they are inferior in transparency, resistance to scratch and bending, and susceptible to scratch during use to thereby increase electric resistance or disconnection of wires, and also inferior in environment resistance at high temperature and high humidity. In particular, in recent years, a market for the touch panels to be used on a smart phone and a car navigator is growing, and the improvement in environment resistance at high temperature and high humidity is strongly desired.
The present inventors have proposed to obtain a transparent conductive laminate improved in transparency, scratch resistance and bending resistance by forming a transparent dielectric thin film such as an SiO2 thin film, on one side of a transparent base film, and a transparent conductive thin film comprising an indium-tin complex oxide, on the SiO2 thin film, and laminating a transparent substrate on the opposite side of the transparent base film via an adhesive layer (refer to reference 3). However, the improvement of environment resistance at high temperature and high humidity is still insufficient with the transparent conductive laminate.
It is effective to increase the thickness of the transparent conductive thin film provided on a transparent base film for improving the environment resistance. However, when the film thickness is increased, the surface resistance of the transparent conductive laminate lowers, so that a surface resistivity suitable for a touch panel cannot be obtained.
[Reference 1] JP 10-330916 A
[Reference 2] JP 2000-81952 A
[Reference 3] JP 2002-326301 A
In consideration of the existing state of things, an object of the invention is to provide a transparent conductive film having a surface resistivity suitable for use such as touch panels and excellent in reliability in high temperature high humidity environment, that is, excellent in humidity and heat resistance.